Sharapova battles through

Maria Sharapova overcame an early scare before advancing to the quarter-finals of the WTA Sony Open in Miami.

The Russian, a five-time finalist in Key Biscayne but never champion, lost the first four games against Kirsten Flipkens before progressing 3-6 6-4 6-1.

The fourth seed won only four points in those first four games and seemed to be thrown by the lack of pace on Flipkens' shots.

However, she gradually found the range with her groundstrokes to turn the match around despite sending down 10 double faults and hitting 36 unforced errors.

"I had a really sloppy start, and Kirsten took advantage," Sharapova said. "I was just making a lot of errors. I'm happy I was able to switch it around."

The Russian will face eighth seed Petra Kvitova for a place in the semi-finals after a remarkable turnaround against former world number one and 12th seed Ana Ivanovic.

The Serbian seemed headed for a quarter-final berth after comfortably taking the first set she fell apart, committing 11 double faults en route to a stunning 3-6 6-0 6-0 loss.

The pair were joined in the last eight by top seed Serena Williams after she brushed aside fellow American Coco Vandeweghe 6-3 6-1 in an hour and 18 minutes on court.

Williams was 4-2 ahead when play was halted due to a rain break, but normal service was swiftly resumed as the veteran collected eight of the next 10 games to go through.

"It was a much tougher match than the scoreline showed," Williams said. "Coco has such an amazing serve, so every time I was returning I was like, 'Hopefully I can touch the ball.' But it was really good for me to win this match."